Project Summary/Abstract Combining high channel count electrophysiological recording of neural activity with patterned electrical micro- stimulation has been severely constrained by technical limitations. Foremost among these limitations are the problems associated with simultaneous recording and micro-stimulation. Stimulation artifacts are up to four orders of magnitude larger than the neural signal being sensed. The large signal drives the amplifiers outside of their linear range and traditional AC coupled amplifiers require long settling times to recover. These long settling times are due to long time constants created by low frequency high pass filters. One traditional approach to avoid amplifier saturation is to employ switches for electrode, headstage amplifier, and stimulator connections to rapidly switch between recording and stimulation. Switches must be employed to disconnect the stimulator when recording to avoid amplifier saturation and degrading the high impedance electrode signal from parasitic cable capacitances and interference sources. This project will develop a research tool for neuroscientists that will achieve electrical stimulation and neural signal recording from the same microelectrode. Multiple channels of simultaneous recording and micro-stimulation from the same electrode are combined on the same integrated circuit (IC) for integration in a headstage. The integration in an IC eliminates signal degradation and interference from cabling and switching parasitic effects. Additionally, the low-noise amplifier circuitry, stimulation circuitry and local control may be intimately tied to mitigate the electrode polarization recovery.